It is known to irrigate fields by laying pipe across the ends of irrigation furrows or ditches, providing openings along a side of the pipe and then filling or partially filling the ipe with water. As the water reaches the level of the openings, it flows out of the holes and into the ditches. This is called gated irrigation pipe.
It is also known to provide valves at the openings which can be adjusted individually to control the flow from each of the openings. This permits control of the flow to adapt the system to varying lengths of the irrigation ditches, changes in elevation of the gated pipe and other variables.
A further development is called "cablegation" in which the pipe is inclined and a plug is passed through the pipe, restrained by a cable and followed by water. By regulating the rate at which the cable is payed out, the speed of the plug is controlled. This controls the length of time the body of water is high enough to reach the openings and, thereby, the amount of water dispensed through each opening.
Examples of irrigation systems in this general category and of valves and couplings usable therein are shown in the following U.S. Pat. Nos.:
______________________________________ 1,043,118 Linxweiler 1,755,104 Deierlein 1,786,963 Schoenberger 3,033,514 Grosch 3,746,263 Reeder et al 3,776,463 Dyck 3,842,859 Reinke 3,880,189 Bennett 3,973,732 Diggs ______________________________________
As will be recognized, it is necessary to adjust the valves from time to time, especially when the system is newly installed but also thereafter as conditions change. It is particularly important to be able to adjust such valves when used in a cablegation system because of the significantly greater potential for water waste by over irrigation or, alternatively, for insufficient irrigation. Thus, it is important that they be easily adjustable and that they remain in the adjusted position despite the influences of wind, surges of water and the activities of small birds and animals. Unfortunately, the valves of the prior art do not satisfy all of those requirements. Some are adjustable only with some difficulty, requiring that a lock nut or screw be loosened to move a valve member. Those which are easily adjustable are also easily movable by, e.g., a field mouse seeking water. Furthermore, valves previously available are not calibrated and, in operation, deliver different flows even in gates which are side-by-side. It is also quite important to be able to control the erosion which can occur as the result of excessive pressure in a stream directed toward the earth.